STUDIES ON THE CARDIAC STOMACH OF A STARFISH, PATIRIA MINIATA (BRANDT)

Abstract

The large cardiac stomach of Patiria, frequently and extensively everted in the feeding behavior of this omnivorous starfish, possesses an unusually elaborate retractor harness. As in Asterias, this consists of an extrinsic part extending from the ambulacral ridge to the stomach wall, and an intrinsic portion spreading over the surface of the stomach in a branching pattern. This intrinsic system consists of 3 interrelated classes of fibers, some muscular, some connective tissue strands, and some mixed. All these accessory components of the retractor harness must have arisen in connection with special problems presented by the size and mode of operation of the cardiac stomach; the several classes of strands, varying in composition and in anatomical relationships, undoubtedly perform specific, different functions in reinforcing, restraining, and retracting the vesicles of the stomach. The wall of the stomach itself has essentially the same histo-logical composition as that usually found in the asteroid digestive tract. Gutter-patterns occur in conjunction with the distribution of some of the intrinsic retractor fibers, and there are specific localizations of various types of epithelial cells in relation to these gutters. In comparison with Asterias, Patiria lacks the conspicuous patches of tall cells with huge, cigar-shaped nuclei and multiple flagella (thought to be sensory receptors) between the gutters; possible explanations may involve differences in feeding habits and the behavior of the stomach between these 2 types of starfishes. Patiria also lacks zymogen cells in its stomach, and when deprived of all its pyloric caeca is unable to digest food. It is concluded that the normal powerful digestive capacities of the stomach involve the action here of enzymes produced by the myriads of zymogen cells in the pyloric caeca.